.wrapper {
  margin-inline: max(0px, ((100% - 64rem) / 2)); 
}

You’d be doing yourself a favor to read Manuel’s breakdown of all what’s happening here, but it basically works out to the equivalent of this longer syntax:

.wrapper {
  max-width: 64rem;
  margin: 0 auto;
  width: 100%;
}

…where:

• max() acecepts a comma-separated list of CSS numeric values, where the applied value is the largest (or as MDN puts it, the “most positive”) one in the set.
• 0px is the first value in the set, ensuring that the smallest value is always going to be greater than zero pixels.
• (100% - 64rem) is the second “value” in the set, but is expressed as a calculation (note that calc() is unnecessary) that subracts the the max-width of the element (64rem) from its full available width (100%). What’s left is the space not taken up by the element.
• ((100% - 64rem) / 2)) divides that remaining space equally since we’re divying it between the inline boundaries of the element.
• max(0px, ((100% - 64rem) / 2)) compares 0px and (100% - 64rem) / 2). The largest value is used. That’ll be the result of the equation in most cases, but if 64rem is ever greater than the computed value of the element’s full 100% width, it’ll lock that value at zero to ensure it never results in a negative value.
• margin-inline is the property that the winning value sets, which applies margin to the inline sides of the element — that’s the logical shorthand equivalent to setting the same value to the margin-left and margin-right physical properties.

It’s the same sort of idea Chris shared a while back that uses the CSS max()function to solve the “Inside Problem” — a container that supports a full-bleed background color while constraining the content inside it with padding.

max(), calc(), margin-inline… that’s a lot of newfangled CSS! And Manuel is right smack dab in the middle of writing about these and other modern CSS features over 100 days.

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Manuel Matuzovic: max() Trickery originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.